Scale effects of supplementary nature reserves on biodiversity conservation in China's southern hilly region

The Southern Hilly Region (SHR) of China plays a critical role in maintaining national ecological security and supporting global biodiversity. However, intensified human activities, such as urbanization and excessive land exploitation, have led to significant ecological degradation, posing threats to both local and global biodiversity. The current nature reserve system in SHR no longer meets the demands for local biodiversity conservation. To address these challenges, this study proposes a strategic framework aimed at enhancing biodiversity conservation in the SHR by establishing Supplementary Nature Reserves (SNRs). Using the Systematic Conservation Planning method, we identified 80 additional SNRs based on existing reserves, focusing on watersheds as the unit of analysis. We evaluated their conservation effectiveness at regional, watershed, and sub-watershed scales. The results indicate that while SNRs significantly improved habitat quality and reduced human impacts at local and smaller scales, their effectiveness varied across spatial scales. The study underscores the importance of multi-scale conservation planning and the need to integrate local and regional strategies to optimize biodiversity protection. These findings provide a foundation for policymakers to develop more targeted and effective conservation measures, ensuring the long-term sustainability of biodiversity in the SHR.